The present study aimed to evaluate nitrate acute toxicity in cultured common snook Centropomus undecimalis juveniles. Fish (20.35±6.10 g and 13.90±1.75 cm) were submitted to a control treatment (without nitrate addition) plus 20 increasing concentrations of nitrate up to 2735 mg L-1 obtained by sodium nitrate. System was semi-static, with 100 % daily water renewed and sodium nitrate addition to maintain the respective concentrations. Water temperature was 20.99±0.55 °C, dissolved oxygen 6.79±0.21 mg L-1, pH 8.23±0.10, alkalinity 141.80±7.68 mg L-1 CaCO3, salinity 33.47±3.75 g L-1, total ammonia and nitrite less than 1 mg L-1. During experimental period (96 h), no mortalities were observed in fish with or without nitrate addition. Compared to other species, the common snook presents higher tolerance to nitrate exposition. Based on the present findings, the acute nitrate exposure up to 2735 mg L-1 does not present lethal risk for common snook juveniles.

As nitrate is the final product in nitrification process, it may reach high concentrations, especially in recirculating aquaculture systems (Hamlin, 2006). In this case, sublethal or lethal effects might occur in fish (Poerch et al., 2007), affecting growth and reproduction (Hamlin et al., 2008), endocrine functions and secondary responses of stress (Hamlin, 2006; Pottinger, 2017) and also histopathologies in gills, esophagus and brain (Shimura et al., 2004; Rodrigues et al., 2011). However, little attention has been given in literature (Rodrigues et al., 2011) and mechanisms of nitrate toxicity are still poorly understood in marine fish (Hamlin, 2006).

Among centropomid fish, the common snook Centropomus undecimalis (Bloch 1972) is one of the most promising species for aquaculture (Souza-Filho and Cerqueira, 2003) and has great potential considering the Brazilian coast (Cavalli et al., 2011). Found in tropical and subtropical estuaries and coastal environments of the Atlantic Ocean (Brennan et al., 2006), it has been studied in America, as the United States (Hauville et al., 2016; Yanes-Roca et al., 2009), Mexico (Ibarra-Castro, Jimenez-Martinez), Colombia (Cruz-Botto et al., 2018), Venezuela (Figueredo-Rodrigues and Fuentes, 2018) and Brazil (Cerqueira et al., 2017; Pedrotti et al., 2018; Michelotti et al., 2018, Passini et al., 2018). Because no information is available about nitrate safe levels for this species, the present study aimed to evaluate nitrate acute toxicity in cultured common snook juveniles.

In this context, acute toxicity tests are important tools for determining nitrate safety levels in aquaculture, especially considering recirculation systems (Rodrigues et al., 2011). Based on the present findings, the acute exposure of nitrate up to 2735 mg L-1 does not present lethal risk for common snook juveniles.